In this work, the preparation of highly thermoresponsive and fully reversible stretch-tunable elastomeric opal films featuring switchable structural colors is reported. Novel particle architectures based on poly(diethylene glycol methylether methacrylate-co-ethyl acrylate) (PDEGMEMA-co-PEA) as shell polymer are synthesized via seeded and stepwise emulsion polymerization protocols. The use of DEGMEMA as comonomer and herein established synthetic strategies leads to monodisperse soft shell particles, which can be directly processed to opal films by using the feasible melt-shear organization technique. Subsequent UV crosslinking strategies open access to mechanically stable and homogeneous elastomeric opal films. The structural colors of the opal films feature mechano- and thermoresponsiveness, which is found to be fully reversible. Optical characterization shows that the combination of both stimuli provokes a photonic bandgap shift of more than 50 nm from 560 nm in the stretched state to 611 nm in the fully swollen state. In addition, versatile colorful patterns onto the colloidal crystal structure are produced by spatial UV-induced crosslinking by using a photomask. This facile approach enables the generation of spatially cross-linked switchable opal films with fascinating optical properties. Herein described strategies for the preparation of PDEGMEMA-containing colloidal architectures, application of the melt-shear ordering technique, and patterned crosslinking of the final opal films open access to novel stimuli-responsive colloidal crystal films, which are expected to be promising materials in the field of security and sensing applications.

are created-with molecular weight (MW), branching, and comonomer distribution being the most important parameters. This is the reason for the incredibly broad spectrum of polymer properties that can be tuned by adjusting a polymeric microstructure on a molecular level. As "polymers are products by process," their microstructure is-to a certain extent-directly controllable via process conditions. [1] This opens up a huge potential of process optimizations as well as aimed product designs for systems with interesting polymeric microstructures that are industrially relevant and fairly well understood. One of those processes is the high-pressure free-radical polymerization of ethylene to low-density polyethylene (LDPE) under supercritical conditions. It is a remarkable example not only because of its high industrial relevance, but mainly because of its complex random branching distribution. The short-and especially long-chain branches (LCBs) impact material properties drastically. [2,3] The LCBs are introduced by an intermolecular transfer reaction of a propagation macroradical to a polymer molecule. The resulting midchain radical can then either undergo a β-scission reaction or propagate further by monomer addition, which forms LCBs. This is shown schematically in Figure 1. Full kinetic schemes of the LDPE polymerization can be found in the literature. [4,5] LCBs are essential when it comes to polymer properties and processing behavior. They lead to effective size reduction of the polymer coil, which can be seen both analytically in light-scattering experiments [6] as well as by studying flow behavior. Rheological experiments show reduced viscosities for LDPE compared to linear high-density polyethylenes. [3,7] However, when the technically relevant strongly nonlinear flows in extension are investigated, LCBs lead to an increased network connectivity in the polymer melt and consequently reduce the rate of disentanglement, if an external force is applied. Thus, a pronounced increase of elongational viscosity with time is observed in extensional flows, which is referred to as strain hardening behavior and very beneficial in terms of processing operations such as blow molding, film blowing, foaming, or fiber spinning. [8] Following this argumentation, understanding structure-property relationships and how they can be manipulated by choosing appropriate reaction conditions is extremely beneficial in the LDPE context. A three-step multi-scale modeling strategy was recently introduced by Pflug and Busch, [4] which demonstrates Reaction conditions have a huge impact on the resulting polymer properties, but capturing this requires understanding the correlation of the underlying kinetics, the polymer architecture, and polymer flow behavior. Long-chain branched polymers created randomly by free-radical polymerization, such as low-density polyethylene (LDPE), show complex rheological behavior and are thus interesting in this context. A study applying a multiscale modeling approach is used to simulate varying reaction condition...

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Two sample sets of low density polyethylene (LDPE) were investigated and differentiated via comprehensive analysis of their microstructures with specific emphasis on branching. The sample sets were produced under well-defined...